Various arrangements have been provided in the past to determine the channel to which a receiver is tuned so that audience share information can be gathered. This audience share information estimates the number of people receiving a program as a percentage of the total audience receiving programs over the same media during the same time slot.
In one example of such arrangements, diaries are furnished to cooperating households having televisions and/or video cassette recorders (VCRs). These diaries are filled out manually by those people who watch or record television programs in the cooperating households. Diaries have several drawbacks, including lack of attention and human error in making diary entries.
Other known systems have been designed to reduce human intervention in the metering of channels to which receivers are tuned. Such channel metering systems typically gather such information as the on-off condition of the receivers being monitored and the identity of the channels to which these receivers are tuned while the receivers are in the on condition. These systems generally store this information for later transmission over telephone lines to a central computer.
In one such channel metering system, the position of a tuning element of a monitored receiver, such as a tuning dial of a receiver, is determined in order to identify the channel to which the monitored receiver is tuned. This system requires a direct mechanical coupling to the tuning element of the monitored receiver. While such mechanical systems are reliable, the direct mechanical coupling of this system requires skilled installation practices. Also, variations in the mechanical configurations of tuner elements between various receivers require a large assortment of adapters to implement direct mechanical couplings. Moreover, most modern day receivers use electronic tuning rather than mechanical tuning so that mechanical coupling arrangements are not practical.
In another known channel metering system, the tuning voltage across a varactor diode of a voltage tunable receiver is monitored in order to determine the channel to which the voltage tunable receiver is tuned. However, this channel metering system is applicable only to voltage tunable receivers.
In yet another known channel metering system, monitoring signals are injected into the tuner of a monitored receiver. Each injected monitoring signal corresponds to one of the channel frequencies to which the monitored receiver can be tuned. The monitoring signals are injected in order of either increasing or decreasing channel frequencies. By detecting which of the injected monitoring signals passes through the tuner of the monitored receiver, the channel to which the monitored receiver is tuned may be determined. In this type of system, care must be exercised to ensure that the injected monitoring signals do not interfere with the program being perceived; otherwise, the enjoyment by the audience of the program may be impaired.
Furthermore, current metering technology is based on the assumption that all states of a tunable receiver, such as that used in a television, a radio, a video cassette recorder, or the like, may be staticly determined. This assumption means, for example, that a unique voltage or combination of voltages, or a unique tuning element position, must be observable for each state of the tunable receiver. Although this assumption has been valid for receivers using analogue technology, it is less valid for digital receivers. Decreasing costs in digital integrated circuit technology has allowed receiver manufacturers to design and manufacture digital receivers. Thus, complex analogue control circuitry can be replaced with a set of integrated circuits or even with a single integrated circuit. The resulting reduction in the number of components of digital receivers increases reliability, reduces manufacturing costs, and simplifies the design of such receivers. Accordingly, the number of digital receivers available to viewing and listening audiences has grown dramatically in recent years. Existing metering systems, which are designed to primarily monitor analogue receivers, are not capable of easily and efficiently monitoring the channels to which such digital receivers are tuned.